Intestinal failure (IF) in define as “the reduction of gut functionbelow the minimum necessary for the absorption ofmacronutrients and/or water and electrolytes, such thatintravenous supplementation is required to maintain healthand/or growth”. The “pathophysiological classification” of IFidentified five major conditions: short bowel, intestinal fistula,intestinal dysmotility, mechanical obstruction, extensive smallbowel (SB) mucosal disease. Short bowel syndrome (SBS) isthe most frequent mechanism of IF. The aim of this paper is tofocus on the aspects of the pathophysiology. In the case ofshort bowel, enterocutaneous fistula or extensive SB disease,the primary mechanism of IF is the malabsorption of theingested food. When an intestinal dysmotility or an intestinalmechanical obstruction occurs, IF is primarily due to therestriction of oral/enteral nutrition or total oral fasting, in orderto limit or avoid the feeding-related exacerbation of digestivesymptoms.